When many molten metals contact air, compounds of those metals, primarily oxides but also nitrides and other non-metallic impurities, can be formed. When the molten metal is moving, the metal and the metal oxide combine to form a material known as dross. The dross often forms a sponge-like network and has a lumpy, granular appearance.
In a wave soldering device, such as that described in U.S. Pat. No. 6,431,431 B2, the disclosure of which is incorporated by reference herein in its entirety, the dross floats on the surface of a molten solder bath. The molten solder is pumped through a nozzle to form a wave. Substrates, such as printed wiring boards, are then passed over and into contact with the wave to deposit solder on the substrate surface. If the dross is allowed to build up, the dross can become entrained in the solder wave and adversely affect the quality of soldering
Accordingly, the dross is periodically removed from the solder reservoir to prevent contamination of the solder. Existing methods of dross removal also often remove a substantial amount of usable molten solder along with the dross. It is estimated that dross removed from the surface of a molten solder bath can included 30-90% usable solder that can be reclaimed for reuse.
Where molten solder has been separated from the dross after removal from the solder reservoir, the molten solder is cooled to form a brick. The brick is then returned to the solder reservoir, where the heat of the molten-solder reservoir re-melts the brick so that the solder is again usable for application to a printed wiring board.